1. Field of the Invention
The present invention relates to a group communication system as a multi-channel access type mobile communication system.
2. Description of the Related Art
A group communication system as a conventional multi-channel access type mobile communication system has been disclosed in Japanese Patent Laid-Open Publication No. Hei 7-30479. According to the related art reference, in a mobile telephone system, a calling party does not directly dial a called party. Instead, a subscriber (called party) with a particular group user radio unit of which the locations of a plurality of called parties have been registered to a mobile communication service center and they are in call receivable state is selected. Calls for connecting with a group communication system are connected with different frequencies. Thus, the frequency use ratio in this system is low.
As another related art reference, in a conventional group communication system that covers a plurality of radio zones, regardless of whether or not mobile stations with relevant group communication numbers are present in a particular radio zone, communication channels are assigned to a radio zone of a base station corresponding to the group communication numbers. Thus, the frequency use efficiency in this system is also low.
In the above-mentioned group communication system, since communication channels are assigned to a radio zone of a base station corresponding to individual group communication numbers, even if a mobile station is not present in an old radio zone due to a hand-over, a communication channel is still assigned to the old radio zone. Thus, the frequency use efficiency is low.
Therefore, an object of the present invention is to provide a group communication system that allows a communication channel assigned to a radio zone to be released in the case that a group communication mobile station is not present in a group communication radio zone so as to improve the frequency use ratio.
To accomplish the above-described object, a group communication system according to the present invention comprises at least one controlling station, at least one base station connected to the controlling station through a wired circuit or a radio circuit, and a plurality of mobile stations connected to the base station, wherein the controlling station or the base station has a means for managing group communication numbers of the mobile stations, wherein the mobile stations each have a means for transmitting a mobile station identification number and a group communication number to the base station when a radio zone of each of the mobile stations is handed over and thereby a location registration operation is performed, wherein the controlling station or the base station has a zone area presence determining means for determining whether or not a particular mobile station is present in a radio zone to which the particular mobile station has been handed over when the controlling station or the base station receives the group communication number from the relevant mobile station, and wherein the base station has a means for releasing a communication channel when the relevant mobile station is not present in the radio zone as the determined result of the zone area presence determining means.
A link line for connecting the controlling station and the base station is preferably provided.
The controlling station is preferably connected to a telephone unit.
The base station and the mobile stations are preferably connected through radio circuits.
The controlling station preferably comprises a controlling portion for connecting the controlling station to the base station, a location registration register portion for registering a location registration signal when the power of the relevant mobile station is turned on or when the radio zone thereof is handed over, and a switching portion for establishing a communication circuit between the relevant mobile station and the wired circuit or the radio circuit through the base station or a communication circuit between the mobile stations.
The location registration register preferably retrieves communication information of the relevant mobile station and certificates whether or not the relevant mobile station has been registered.
The controlling portion is preferably connected to the location registration register portion and the switching portion.
The base station preferably comprises a controlling portion connected to the controlling portion of the controlling station, a control channel transmitting/receiving portion connected to the location registration register portion of the controlling station, and a transmitting/receiving unit with plurality of communication channels.
The control channel transmitting/receiving unit preferably controls the mobile stations.
According to the present invention, in a group communication system comprising at least one controlling station, at least one base station connected to the controlling station through a wired circuit or a radio circuit, and a plurality of mobile stations connected to the base station, wherein the controlling station or the base station has a function for managing group communication numbers of the mobile stations, wherein the mobile stations each have a function for transmitting a mobile station identification number and a group communication number to the base station when a radio zone of each of the mobile stations is handed over and thereby a location registration operation is performed, wherein the controlling station or the base station determines whether or not a particular mobile station is present in a radio zone to which the particular mobile station has been handed over when the controlling station or the base station receives the group communication number from the relevant mobile station, and wherein the base station releases a communication channel when the relevant mobile station is not present in the radio zone as the determined result.
The group-communication group-number management register disposed in the controlling station or the base station manages group communication calls and collates them with group communication numbers as information of location registration signals transmitted from mobile stations.
In addition, since the group-communication group-number management register disposed in the controlling station or the base station can manage group communication calls, it can determine whether or not a particular mobile station that can be moved in a plurality of radio zones is present in the radio zone of the controlling station or the base station. Thus, the controlling station or the base station does not assign a radio channel to a radio zone in which a group communication mobile station is not present.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawings.